The present invention relates generally to devices for implantation within a patient""s body, particularly to pressure sensors that may be implanted within a body, and more particularly to implantable pressure sensors that may be energized, activated, controlled, and/or otherwise communicate via acoustic energy.
Devices are known that may be implanted within a patient""s body to monitor one or more physiological conditions and/or to provide therapeutic functions. For example, sensors or transducers may be located deep within the body for monitoring a variety of properties, such as temperature, pressure, strain, fluid flow, chemical properties, electrical properties, magnetic properties, and the like. In addition, devices may be implanted that perform one or more therapeutic functions, such as drug delivery, defibrillation, electrical stimulation, and the like.
Often it is desirable to control such devices once they are implanted within a patient by external command, for example, to obtain data, and/or to activate or otherwise control the implant. An implant may include wire leads from the implant to an exterior surface of the patient, thereby allowing an external controller or other device to be directly coupled to the implant. Alternatively, the implant may be remotely controlled, e.g., using an external induction device. For example, an external radio frequency (RF) transmitter may be used to communicate with the implant. RF energy, however, may only penetrate a few millimeters into a body, because of the body""s dielectric nature. Thus, RF energy may not be able to communicate effectively with an implant that is located deep within the body. In addition, although an RF transmitter may be able to induce a current within an implant, the implant""s receiving antenna, generally a low impedance coil, may generate a voltage that is too low to provide a reliable switching mechanism.
In a further alternative, electromagnetic energy may be used to control an implant, since a body generally does not attenuate magnetic fields. The presence of external magnetic fields encountered by the patient during normal activity, however, may expose the patient to the risk of false positives, i.e., accidental activation or deactivation of the implant. Furthermore, external electromagnetic systems may be cumbersome and may not be able to effectively transfer coded information to an implant.
Accordingly, a sensor, such as a pressure sensor, that may implanted within a patient""s body, and may be energized by, controlled by, and/or otherwise communicate effectively with an external interface would be considered useful.
The present invention is generally directed to implants that may be implanted, e.g., using open surgical or minimally invasive techniques, or otherwise located within a mammalian body for monitoring pressure or other physiological parameters and/or for performing one or more therapeutic functions.
In accordance with a first aspect of the present invention, an implant is provided that includes a pressure sensor for measuring intra-body pressure. A controller is coupled to the pressure sensor for acquiring pressure data from the pressure sensor. One or more acoustic transducers are provided for converting energy between electrical energy and acoustic energy. Preferably, the one or more acoustic transducers are configured for converting acoustic energy from a source external to the implant into electrical energy and/or for transmitting an acoustic signal including the pressure data to a location external to the implant. One or more energy storage devices are coupled to at least one of the one or more acoustic transducers, the energy storage device(s) configured for storing electrical energy converted by the one or more acoustic transducers. The energy storage device(s) may be coupled to the controller for providing electrical energy to support operation of the implant. The energy storage device may include one or more capacitors, for example, a first relatively fast-charging capacitor and a second relatively slow-charging capacitor. In addition or alternatively, the energy storage device may include a rechargeable and/or nonrechargeable battery.
In a preferred embodiment, the one or more acoustic transducers may be a single transducer configured to operate alternatively as either an energy exchanger or an acoustic transmitter. Alternatively, the acoustic transducers may include an acoustic transmitter coupled to the controller for transmitting the acoustic signal to a location external to the body. In addition or alternatively, the acoustic transducers may include an energy exchanger coupled to the energy storage device, the energy exchanger including a piezoelectric layer for converting acoustic energy striking the piezoelectric layer into electrical energy.
The components of the implant may be attached to a substrate, such as a printed circuit board (PCB), and may be secured within a casing. The casing may include one or more openings through which active areas of the pressure sensor and/or the energy transducer may be exposed to a region exterior to the casing. Alternatively, the active area of the pressure sensor may be covered with a seal, such as silicone, Parylene C, or a relatively thin metal layer. In a further alternative, the casing may include a relatively thin foil or thin-walled region for sealing at least one of the pressure sensor and the energy transducer from a region exterior to the casing. The casing may be filled with a fluid, gel, and/or low modulus material, such as silicone, for coupling the pressure sensor and/or the energy transducer to the foil or thin-walled region. Thus, the thin-walled region may be used to couple the pressure sensor and/or energy transducer to a region exterior to the casing.
In accordance with another aspect of the present invention, a method is provided for making an energy exchanger for converting between acoustic and electrical energy. First, a layer of piezoelectric polymer is provided, such as a fluorocarbon polymer, preferably poly vinylidene fluoride (PVDF), or a copolymer of PVDF, such as PVDF-TrFE. The layer of polymer may be etched, e.g., to cleave carbon-fluorine, carbon-hydrogen, and/or carbon-carbon bonds, for example, using a sodium naphthalene solution (for carbon-fluorine bonds), or using a gas phase plasma treatment including oxygen, air, Argon, Helium, and/or other gas plasma (e.g., SF6). A conductive layer may be applied onto the layer of polymer. The layer of polymer generally includes first and second surfaces, and first and second conductive layers are applied onto the first and second surfaces of the layer of polymer.
An adhesive, such as an epoxy or acrylic adhesive, is applied, e.g., atomized, over a substrate including one or more cavities therein. The piezoelectric layer is applied to a surface of the substrate. Pressure may be applied between the piezoelectric layer and the substrate, thereby causing the piezoelectric layer to become at least partially depressed within the one or more cavities. The adhesive may be cured, for example, using heat and/or pressure, and/or by exposure to visible or ultraviolet light.
The energy exchanger may then be incorporated into an implant, such as that described above. A substrate, e.g., a printed circuit board (PCB), e.g., made from FR4, Rogers, ceramic, Kapton, Teflon, PVDF, and/or PEEK, may be provided having an opening therethrough. A pressure sensor may be attached to the substrate adjacent the opening, the pressure sensor including an active area exposed via the opening for measuring intra-body pressure. A controller may be attached to the substrate and coupled to the pressure sensor for acquiring pressure data from the pressure sensor. An energy exchanger may be attached to the substrate, the energy exchanger coupled to the controller for at least one of converting acoustic energy from a source external to the implant into electrical energy and transmitting an acoustic signal, e.g., including the pressure data and optionally other information, to a location external to the implant. Finally, an energy storage device may be attached to the substrate and coupled to the energy exchanger, the energy storage device configured for storing electrical energy converted by the acoustic transducer and/or for providing electrical energy to support operation of the implant. The substrate and attached components may then be received in a casing for sealing the implant.
In accordance with yet another aspect of the present invention, a method is provided for acquiring data from an implant, such as that described above, that is implanted within a patient""s body, using an external transducer located outside the patient""s body. Generally, the external transducer transmits a first acoustic signal into the patient""s body, the first acoustic signal being converted into electrical energy for operating the implant. The first acoustic signal may include an identification code (e.g., a serial number, model number, and/or other identifier) identifying a target implant, or other information, which may be interpreted by the implant. The implant may confirm that the identification code matches the implant, whereupon the implant may sample data and transmit a second acoustic signal to the external transducer.
In response, the external transducer receives the second acoustic signal from the implant, the acoustic signal including data related to a condition with the patient""s body measured by the implant. Preferably, the external transducer automatically switches from an energizing mode after transmitting the first acoustic signal to a receiving mode for receiving the second acoustic signal. Upon completion of transmitting the data, e.g., after a power level of the implant falls below a predetermined level and/or after a predetermined time, the implant returns to a passive mode, awaiting further energizing or activation by the external transducer. Alternatively, after receiving the second acoustic signal, the external transducer may automatically switch back and forth from the energizing mode to the receiving mode, thereby alternately energizing the implant and receiving data from the implant. For example, the external transducer may transmit an energizing signal during any pause in operation of the implant, e.g., whenever the energy exchanger is available to receive the energizing signal. This may allow the external transducer to maintain the implant substantially fully charged, thereby allowing substantially indefinite operation. In a further alternative, the first and second acoustic signals may be transmitted simultaneously, e.g., at different frequencies.
In an alternative embodiment, the first acoustic signal transmitted by the external transducer may be a diagnostic signal, e.g., including a broad band signal or a scanning signal, that may be used to determine an optimal frequency for communicating with the implant. The implant may transmit at different frequencies in response to the diagnostic signal, and the external transducer may determine the optimal frequency for communicating with the implant. Alternatively, when the implant detects the diagnostic signal at an optimal frequency, it may respond with a second acoustic signal identifying or merely transmitting at the optimal frequency.
In yet another alternative embodiment, the energy storage device of the implant may include a relatively fast-charging device and a relatively slow-charging device. When the implant receives a first acoustic signal, it may immediately charge the fast-charging device, thereby allowing the implant to transmit a prompt response to the external transducer, e.g., within about fifty to two hundred milliseconds or less. The transmitted response may include an identification code, a confirmation that the implant is operational, and the like. While the implant is responding, the slow-charging device may continue to charge, e.g., to support subsequent operation of the implant during data sampling and transmission.
Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.